AMORPHOUS SILICA - A REVIEW OF HEALTH-EFFECTS FROM INHALATION EXPOSURE WITH PARTICULAR REFERENCE TO CANCER

Silicas and silicates are some of the most abundant compounds found na turally in the earth's crust. Excessive exposure to crystalline silica s can cause serious lung disease such as silicosis and has been associ ated with lung cancer in some studies, but the potential health effect s of amorphous silicas (silicon dioxide without crystalline structure) have not been well studied. Results from animal studies of amorphous silicas, unlike those seen with crystalline silicas, have suggested li mited and largely reversible cytotoxic and possibly fibrogenic effects associated with some forms, but data on cancer outcomes are scanty an d for the most part negative. Epidemiologic investigations to date for any potential cancer risk are not informative because the effects of crystalline and amorphous silicas have not been separated. Any future epidemiologic study should attempt to clarify the health effects of am orphous silicas from those of crystalline silicas, particularly with r egard to any potential for carcinogenicity.